The continuation of this program will include: a) studies of mother-infant interactions in the chimpanzee with specific emphasis on individual differences in mother-infant relationships and studies on the behavioral and physiological responses to brief separation in squirrel monkeys; b) studies on juvenile chimpanzees and squirrel monkeys with emphasis on sex differences in prepubescent animals. Play behavior and the role of gonadal hormones on the regulation of play will be investigated; c) studies on the psychobiology of adolescence in both chimpanzee and squirrel monkey, with emphasis on the relationship between changes in behavior during the adolescent transition period and change in hormonal states which occur as a consequence of puberty; and d) studies on the relationships between hormones and adult social behavior. These studies will include investigations of the hormonal changes which occur in dominance/subordinate relationships and the role of the gonadal hormones in the maintenance and regulation of squirrel monkey social organization. We are proposing a life history approach which studies the animals longitudinally through distinct stages of development and, further, focuses on specific stages of development to obtain detailed information on the relationship between hormones and social behavior.